Molecular still



Oct. 15, 1968 W. s. PORT ET AL, 3,406,097

MOLECULAR STILL Filed Jan. 17, 196

/N VEN TOR WILLIAM S. PORT CHARLES K. CHIKLIS A TTRNEYS United States Patent4 O 3,406,097 MOLECULAR STILL William S. Port, Andover, and Charles K. Chiklis, Lexington, Mass., assignors to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Jan. 17, 1966, Ser. No. 520,954 3 Claims. (Cl. 202-190) ABSTRACT F THE DISCLOSURE The invention covers a molecular still having an evaporation compartment defined by vertical walls and Aa top and bottom wall. The bottom wall has a planar roughened surface inclined from to 15 degrees with the horizontal. Heating means is provided on the undersurface of the bottom wall to heat the top surface for evaporating drops of material that are dropped on the top surface.

This invention relates to distillation apparatus, and more particularly to a device for distillation of heat sensitive compounds.

In various distillation processes, such as employed in the producing of pharmaceuticals and in polymer research, there is a need to provide apparatus for the distillation of materials which are heat sensitive. By heat sensitive it is meant that the material will decompose. polymerize or otherwise change structurally under high thermal conditions. Various types of molecular stills have been provided in the past for accomplishing this purpose. However, a great number of these devices have proved inadequate in performance, while those that are generally acceptable in operation are relatively expensive to manufacture.

One type of apparatus which may rbe used for this purpose is commonly known in the art as a Hickman still. While this device is a relatively inexpensive and simple piece of equipment, it is sometimes found to be inadequate in that only.sma1l batches of material may *be distilled at a single operation. This is in part due to the lack of provision for removal of undistilled material from the heating zone.

The present invention is directed to a molecular still of the Hickman type, which has incorporated therein novel features designed to provide an improved distillation apparatus, thus resulting in an improved end product.

It is therefore an object of the present invention to provide distillation apparatus of the molecular still type wherein a residue of undistilled material is continuously removed from the heated zone during the distillation process.

Another object of the invention is to provide distillation apparatus wherein a substantially new surface of the liquid to be distilled is constantly provided at the heated zone of the apparatus.

A further object of the invention is to provide a molecular still which achieves the above objectives yet is both simple and economical in design and manufacture.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a speciiic embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a sectional elevational view showing a component of a molecular still having one embodiment of the invention provided therein;

FIGURE 2 is a bottom plan view showing an alternate ICC embodiment of a portion of the structure shown in FIG- URE 1; and

FIGURE 3 is a sectional elevational view, similar to a portion of FIGURE 1 showing an alternate arrangement of that structure.

Referring to the drawings, especially FIGURE l, there is shown an evaporative component 10 of a molecular still having an upper, substantially enclosed, chamber 11 and -a lower chamber 12 which is open at the bottom. The chambers 11 and 12 are partially defined by a cylindrical wall 13 and chamber 11 has a top wall 14, and a bottom w-all 15 which further serves to divide chamber 11 from chamber 12.

Near the top of the cylindrical wall 13, there is formed an opening 16 connec-ting with a tubular portion 17 which generally leads from a feed ask (not shown) containing the liquid to be distilled.

Adjacent the bottom of the chamber 11, the cylindrical wall 13 is provided with an opening 18 connecting with another tubular portion 19. The opening 18 has its lower portion at the same level as an adjacent portion of the top surface 21 of the wall 15, such that unrestricted flow may take place from the surface into the tube 19. The tube 19 is connected to a run-off ask (not shown) disposed below the surface 21 to provide gravity flow.

IIn addition to the openings 16 and 18 previously described, a third opening 22 is provided in the cylindrical wall 13. The opening 22 exits outwardly into a tubular portion 23 `and a tubular member 24 extends inwardly from the opening to a point approximately at the center of the chamber 11. As will be noted, the tubular member 24 is terminated in the chamber 11 by an upwardly facing opening 26 provided therein. At the opposite end the tube 24 is connected such as to open directly into the tu'bular member 23 which in turn opens into a distillate receiver (not shown).

Referring back to the top wall 14 of the component 10, it will vbe noted that the wall has a generally downwardly-inwardly sloping surface 27 which terminates in an apex 28 just above the opening 26. While the top wall 14 as 4shown has .a generally radial configuration terminating in the apex 28, it will be obvious from the following description that the surface 27 could be a conical surface and still function in the desired manner as will be apparent as the description proceeds.

Returning now to the lower portion of the component 10, it will further be noted that the lower chamber 12 is provided with a ring-type heater 31 which may be connected to an adjustable voltage source through leads L1 `and L2 for varying the Iheater temperature. The ringtype heater 31 is a type well known in the `art and is connected adjacent the lower surface of the bottom wall 14 by using a heat resistant adhesive or by any other suitable fastening means.

In the embodiments shown in FIGURES l and 3, a thin sheet 32 which may be fabricated from asbestos or other insulating material is provided between the heater 31 and the lower surface of the wall 15. The use of the sheet 32 aids in providing a more uniform, evenly distributed heat to the wall 15.

Additionally, the lower surface of the wall 15 is provided with heat sensing means in the form of a thermocouple 33 embedded at the interface between the sheet 32 and the wall 15. The thermocouple 33 is connected by suitable connections L3 to monitoring equipment for reading the temperature at the interface.

Both FIGURE 2 and FIGURE 3 show alternate arrangements for providing uniform heat to the surface 21 through the wall 15.

Referring now to FIGURE 2, there is shown a wall 15a similar to the Wall 15 of FIGURE l. As an alternate vwell known for use in such applications. A pair of terminals 36 and 37 are provided for connecting the coating '34 to a 4voltage source through leads such as L1 and L2,

-and the coating 34 is of such a pattern as to uniformly heat the Wall a.

v Referring to FIGURE 3 where like parts have been given like reference numerals as in FIGURE 1, yet another heating arrangement is shown. Here, the bottom wall 15 is provided with a cylindrical block 3S fabricated ofbrass or similar heat conducting material. The block 38 is'disposed adjacent the bottom'surface of the wall 15 and is separated from the wall by sheet 32 in a similar manner as in FIGURE 1. In the block 38 there is found an opening 39 for receiving a heater 41.` The heater is arod type lheating element which Yis well known in the art, and is so disposed for transferring heat to the block 38 which in turn transfers the heat in a uniform manner to the Wall 15.

In operation of the still, the material to be distilled is held in a flask or other container having an opening connecting to the tubular portion 1'7 of the component 10. The entire system including the feed flask (not shown) and the chamber y11 are evacuated to a desired pressure by a vacuum pump which may be attached to the tubular portion 23.

4'. of the tubular member 24. From the, tubular member 24 the distillate flows through the opening 22 into the tubular portion 23 which is connected to a distillate received in the form of a ask (not shown).

If the conditions of temperature and pressure are not adequate to produce distillation of the material impinging upon thesurface 21, the material will flow down hill due tovgravity through the opening 18 into the tubular portion 19. The tubular portion ,19 is generally connected to a run-off flask (notshown) Ainwhijch the-undistilled material is collected.

As should be evident from the previously description of operation, the apparatus disclosed provides a device highly effective for the distillation of those heat sensitive materials requiring a `fast thermal contact during the distillation process. l j

The uses of the ,molecular s till 10 are quite general, but it is particularly effective vin the purification offliigh molecular weight diepoxides such as those used in thermosetting resin technology. Its effectiveness is generally-attributable to the tilted surface 2.1 whichl minimizes material residence times on the heated surface and thereby reduces the possibility of homo-polymerization.

The following analytical data shown in Table I are given on a commercially available epoxy resin before and after two passes through the device described. This cornmercial product s basically the diglycidyl ether of bisphenol A plus some percentage of lhigher-weight homologs and can be represented by the formula:

The heater 31 (or 36 and 34 in their particular embodiments) is energized by applying a voltage across the lines L1 and L2 which may be regulated by a transformer to control the temperature produced. The temperature of the interface between the sheet 32 and the wall 15 is now monitored by the thermocouple 33, and the voltage regulated until the proper distillation temperature has been reached.

When the wall 15 is at the proper temperature, a few drops of liquid from the feed flask are allowed to flow into the tubular portion 17 to the chamber 11 through the opening 16. The drops o-f material fall on the heated surface 21 of the Wall 15.

It should here be noted that the surface 21 of the wall 15 is tilted such that it forms an acute angle ql with a horizontal plane designated at |I-I in FIGURE 1. The material to be distilled therefore impinges on the surface 21 and is caused to flow down the substantially inclined plane of the surface, due to gravity. A surface angle 45 in the area of 5 to 15 has proved successful in operation, however it should be shown that this angle may vary according to the material to be distilled.

It should also here be mentioned that the surface 21 is generally ground to a predetermined, roughened condition to further control ow of material over the surface. In practice, the desired roughness may be imparted to the surface 21 by polishing the surface on a grinding plate using 120 grit silicon carbide.

The roughness of the surface 2.1 thus produced facilitates spreading of the droplets over the surface, as the flow is retarded with an increase in surface roughness. This feature in combination with the inclined surface defined by the acute angle qb thus prevents the droplets from combining at a single point to form bumps on the material to be distilled.

With the droplets of material impinging on the surface 21, should the conditions of temperature and pressure be adequate Ifor distillation, the droplets will distill to the cold condensing surface Z7 of the wall 14. Due to the inclined `surface of the wall 14 the distillate flows to the apex 28 and thence falls as droplets into the opening 26 Here, the objective was to obtain, by molecular distillation the pure diglycidyl ether of bis-phenol A(lt=0).

TABLE I.-ANALYTICAL DATA 0N AN EPOXY RESIN BEFORE AND AFTER MOLECULAR DISTILLATION 1 Chemically bound chlorine.

As will be noted, the second distillation yielded a product which analyzed very close to the theoretical values.

It should therefore be obvious from the preceding that the present invention provides distillation apparatus which is effective in achieving the various objectives as set forth. In addition, the device may be simply and economically manufactured employing Pyrex or other inexpensive high temperature resistant material.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be vachieved without departing from the spirit and scope 0f the invention as defined by the following claims.

We claim:

1. In a molecular distillation apparatus the combination of;

a plurality of walls defining a substantially enclosed chamber and including a top and a bottom wall, said chamber walls having an opening provided therein for entry into said chamber of material to be distilled, l said walls having means for the removal of distillate from the chamber, t said top wall comprising a cold wall for condensing distillate vapors of the material being/distilled,

said bottom wall having a roughened planar surface forming an acute angle with a horizontal plane and facing upwardly and inwardly with respect to said chamber for removal of undistilled material from said chamber by gravity flow, and said walls further having an opening provided therein and disposed adjacent the lowermost portion of said bottom wall surface to drain undistilled material from said chamber during the distillation process,

said apparatus including a heating means arranged beneath the bottom wall, a thin sheet of heat insulating material disposed beneath the bottom wall and contiguous with the undersurface of the bottom wall to distribute heat evenly to the undersurface, and temperature measuring means for determining the temperature at the interface of said sheet and bottom wall.

2. The combination of claim 1 in which said planar surface is provided with a pre-determined roughness to control the ow of material thereover.

3. The combination of claim 1 which is further characterized by said planar surface forming an angle with the horizontal, which angle is in the range of from 5 to 15.

References Cited UNITED STATES PATENTS 388,278 8/1888 Home 202-205 X 1,885,402 11/1932 Angelucci 202-205 X 2,117,802 5/1938 Hickman 202-161 X 2,234,166 3/1941 Hickman 202-205 2,538,957 l/l95l Askevold et al. 202-161 X 3,190,816 6/1965 Adamec 202-234 2,446,997 8/1948 Brewer et al. 203-81 X 2,554,703 5/1951 Hickman 202-236 X OTHER REFERENCES 1nd. and Engineering Chemistry (1943), vol. 15, #1, pp. 81 and 82.

0 NORMAN YUDKOFF, Primary Examiner.

F. E. DRUMMOND, Assistant Examiner'. 

